Coating liquid, composite particle manufacturing method, and composite particle

Abstract

The coating liquid includes a solute and a solvent. The solute comprises a phosphoric acid compound. “I0/(I0+I1+I2)” is 0.7 or less. In the 31P-NMR spectrum, I0 indicates the area of the signal from the PO4, Q0 unit, I1 indicates the area of the signal from the PO4, Q1 unit, and I2 indicates the area of the signal from the PO4, Q2 unit.

What is claimed is: 
     
         1 . A coating liquid comprising:
 a solute; and   a solvent,   wherein the solute includes a phosphoric acid compound,   wherein a relationship of the following formula (1) is satisfied:
   { I   0 /( I   0   +I   1   +I   2 )}≤0.7  (1),
 
   wherein in the above formula (1),
 I 0  indicates an area of a signal from a Q 0  unit of PO 4  in a  31 P-NMR spectrum, 
 I 1  indicates an area of a signal from a Q 1  unit of PO 4  in the  31 P-NMR spectrum, and 
 I 2  indicates an area of a signal from a Q 2  unit of PO 4  in the  31 P-NMR spectrum. 
   
     
     
         2 . The coating liquid according to  claim 1 , wherein a relationship of the following formula (2) is further satisfied:
   0.17≤{ I   2 /( I   0   +I   1   +I   2 )}  (2).
   
     
     
         3 . The coating liquid according to  claim 1 , wherein a relationship of the following formula (3) is further satisfied:
     I   0   <I   2   (3).
   
     
     
         4 . The coating liquid according to  claim 1 ,
 wherein a relationship of the following formula (4) is further satisfied:
   0≤ C   Li   /C   P <1.1  (4), and
 
   wherein in the above formula (4),
 C Li  indicates a molar concentration of lithium in the coating liquid, and 
 C P  indicates a molar concentration of phosphorus in the coating liquid. 
   
     
     
         5 . The coating liquid according to  claim 1 , wherein the solvent includes water. 
     
     
         6 . The coating liquid according to  claim 1 , wherein the solute includes at least one selected from a group consisting of metaphosphoric acid and polyphosphoric acid. 
     
     
         7 . The coating liquid according to  claim 1 , wherein the solute further includes sodium. 
     
     
         8 . A composite particle manufacturing method comprising:
 (a) preparing a mixture by mixing the coating liquid according to  claim 1  and a positive electrode active material particle; and   (b) manufacturing a composite particle by drying the mixture,   wherein the composite particle includes the positive electrode active material particle and a coating film,   wherein the coating film covers at least a part of a surface of the positive electrode active material particle, and   wherein the coating film includes phosphorus.   
     
     
         9 . The composite particle manufacturing method according to  claim 8 , wherein (b) includes forming the composite particle by a spray drying method. 
     
     
         10 . A composite particle comprising:
 a positive electrode active material particle; and   a coating film,   wherein the coating film covers at least a part of a surface of the positive electrode active material particle,   wherein the coating film includes phosphorus,   wherein the coating film has a thickness of 28.5 nm or less, and   wherein a coverage ratio measured by X-ray photoelectron spectroscopy is 83% or more.